Method and apparatus for producing sound pulses within bore holes

ABSTRACT

An impulse sound source for geophysical studies of the earth for oil, gas and other natural resource exploration and more specifically a streamlined design of a hydraulically controlled sound source that may be inserted into oil wells and bore holes for analysis of geological formations deep beneath the earth&#39;s surface.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/713,945 filed Oct. 15, 2012 entitled Method and Apparatus for Producing Sound Pulses Within Bore Holes which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention is an impulse sound source for geophysical studies of geological structures surrounding bore holes.

BACKGROUND OF THE INVENTION

Geophysical surveys provide a cross-sectional map of the geology below the surface of the earth. Using sound waves, the shape and character of the geology may be revealed to indicate pockets within the sedimentary layers where oil and gas may be trapped, indicating locations where exploratory wells may be drilled for further geological analysis. Geophysical studies between bore holes or between bore holes and the ground surface have been done in the past using small charges of explosive impulsive sources and vibratory sound sources, but none of these types of sound sources have proved to be either practical or robust enough to be used over extended periods of time. An impulsive type of down-hole sound source designed to be robust as well as provide a practical tool to provide sound pulses for geophysical studies of the earth surrounding bore holes is here-with provided.

SUMMARY OF THE INVENTION

The present invention is an impulse sound source that utilizes a free piston which is accelerated by the hydrostatic pressure of a fluid. Upon actuation of the free piston, the free piston moves through an isolated partially fluid filled piston chamber and strikes a sound transmitting anvil sending a sound pulse into an adjacent sound transmission chamber that is filled with light weight oil and surrounded by an elastomeric bladder. The sound pulse from the accelerating anvil moves the elastomeric bladder producing a sound wave that is emitted out through the fluid and ambient walls of the bore hole and into geological surrounding structures. In preparation for firing, an electric motor powered hydraulic pump, pumps hydraulic fluid to move a reset piston assembly to position a latching seal flange of the assembly into a receiving cup of a free piston. A check valve assembly within the flange provides for the evacuation of fluid within the receiving cup forming a vacuum seal that allows the reset piston assembly to draw the free piston through a high pressure fluid filled chamber and into a ready to fire position. The free piston is drawn to a stop point that breaks the vacuum and allows high pressure fluid within the chamber to rapidly accelerate the free piston against the anvil piston with the impulse providing the sound transmission.

The impulse sound source is designed in sections aligned end to end with a first cable termination module housing an umbilical cable and providing for the cable to be attached to and detached from the source. The cable is terminated at a two piece connector that has a first half portion within the upper module detachable from a second half portion that is mounted within the next module, an expansion chamber. The expansion chamber is enclosed with an elastomeric bladder to provide for changes in pressures within the source and assist in the absorption of vibrations as the source is fired. The expansion chamber serves as a reservoir for hydraulic fluid to operate the reset piston assembly. The expansion chamber also houses a set of power cables that extend through the chamber and are affixed to run an electric motor housed in the next module. The electric motor drives a hydraulic pump housed within a next module. The hydraulic pump takes fluid from and returns fluid to the reservoir of the expansion chamber and provides fluid to move the reset piston assembly that prepares the source for firing. The reset piston assembly module also houses the high pressure fluid implosion chamber for the free piston. The impact chamber is an open cylinder that houses the anvil and receives the fired free piston from the implosion chamber that strikes the anvil forcing the anvil a short distance into the sound transmission chamber transmitting the sound pulse to the elastomeric bladder that encloses the transmission chamber. The bladder propagates the sound through the fluid of the bore hole and the surrounding geological structure.

The reversible three phase or DC motor is capable of high temperature operation and provides for the source to be successively fired as the motor is rotated in a first direction to supply hydraulic fluid to move the reset piston down to retrieve the free piston and an opposite direction to draw the free piston up to a ready to fire position with the rate of firing controlled by the speed of the motor. The motor direction is reversed using a relay switch that switches the power leads when the motor amperage peaks due to the latching seal flange bottoming out within the receiving cup in an extended position of the reset piston assembly or to switch directions when abutting a bulkhead of the reset piston assembly housing in a fully retracted position. In further embodiments, the electric motor may be controlled remotely electronically controlled to set the speed of the motor and firing rate.

The modular design of the impulse sound source provides for the top surface of the anvil and bottom surface of the free piston cylinder to be interchanged with anvils and free pistons of different shapes and sizes to change the characteristics of the sound pulse. For example, two flat shapes of the piston and anvil surfaces may produce the sharpest energy transition with the greatest amplitude and highest frequency upon impact of the free piston and the anvil piston. However, if the free piston shape is instead shaped as a conical point mating with the anvil having a conical hole, the frequency content would change as the conical point enters the conical hole producing a longer pulse with lower frequency content in the sound pulse with various shapes producing a range of amplitudes and frequencies.

The impact chamber is further partially filled with fluid to create a cushion for the free piston and the anvil preventing the contact of metal on metal and absorbing vibrations within the source. The sound characteristics may be further changed by the compressibility and type of fluid used within the impact chamber. Fluids of different viscosity and compressibility may change compression characteristics of the fluid. For example, a more compressible fluid may slow the acceleration of the free piston and therefore produce a lower frequency pulse. The impulse source may further be of any diameter and length necessary to accommodate the diameter of the bore hole and requirements of the geological survey.

The present invention is further related to an impulse sound source comprising an umbilical cable extending through a cylindrical housing; a hydraulic fluid reservoir formed within the housing and supplying an hydraulic pump; an electric motor powered from the umbilical cable and controlling the hydraulic pump; a hydraulic cylinder controlled by the hydraulic pump; a reset piston movable within a fluid filled piston chamber using the hydraulic cylinder, the reset piston having a flange movable within an implosion chamber; a free piston having an annular rim and cup within the implosion chamber; an anvil within an impact chamber adjacent the implosion chamber; an elastomeric bladder enclosing a fluid filled sound transmission chamber adjacent the impact chamber; and wherein the free piston is accelerated by hydrostatic pressure within the implosion chamber to strike the anvil and transmit a sound pulse through the sound transmission chamber and the elastomeric bladder.

The impulse sound source further comprises a latching seal assembly surrounding the reset piston flange, the flange having an inlet passage and check valve to evacuate fluid from the free piston cup and thereby latch the reset piston and free piston to draw the free piston to a ready to fire position. The difference in cross-sectional area of the reset piston flange and free piston annular rim provides the clamping force for the reset piston to latch to the free piston. The impulse sound source may be repeatably fired by having the reset piston retract to an uppermost position causing the electric motor to rotate in a first direction to control the delivery of hydraulic fluid from the hydraulic pump to a first chamber and return hydraulic fluid to the reservoir from a second chamber and move the reset piston to the free piston and wherein the reset piston and free piston latch triggering the electric motor to reverse direction and the delivery of hydraulic fluid from the hydraulic pump is to the second chamber and return of hydraulic fluid to the reservoir is from the first chamber to move the reset piston and free piston to the uppermost position where the free piston is fired and the electric motor is triggered to rotate in the first direction.

The impact chamber of the impulse sound source may be partially filled with fluid and changing the viscosity and compressibility of the fluid within the impact chamber changes the characteristics of the sound pulse. In the impulse sound source, the shape of a bottom surface of the free piston and the shape of the top surface of the anvil changes the characteristics of the sound pulse where as an example the top surface of the anvil may be recessed in shape and the shape of the free piston may be conical. The impulse sound may further have a dashpot in the anvil. The implosion chamber of the impulse sound source may further comprise an elastomeric bladder to conform to fluid movements within the impulse sound source. The reservoir of the impulse sound source may further comprise an elastomeric bladder to conform to fluid movements within the impulse sound source. Components of the impulse sound source may be arranged in the order of an umbilical termination module on the top, an expansion chamber module beneath, next an electric motor housing module beneath, next a hydraulic pump module beneath, next an hydraulic cylinder module beneath, next a free piston implosion module beneath, next an impact chamber module beneath, and next a sound transmitting module beneath.

The impulse sound source may further comprise a manifold block adjacent to the hydraulic pump and the manifold block may house two pressure relief valves and two check valves. The reset piston of the impulse sound source may be directly attached to a hydraulic piston rod on the opposite side of a hydraulic cylinder bulkhead. The sound transmitting anvil of the impulse sound source may have fluid flow passages for fluid volume control.

The present invention is further related to a method of generating a sound pulse within a bore hole, comprising the steps of extending an umbilical cable to support a cylindrical housing of a sound source; storing hydraulic fluid in a reservoir within the housing; supplying a hydraulic pump from the reservoir; controlling the hydraulic pump using an electric motor powered from the umbilical cable; filling a hydraulic cylinder using the hydraulic pump; moving a reset piston within a fluid filled implosion chamber using the hydraulic cylinder; seating the reset piston within a cup formed in the upper portion of a free piston; evacuating fluid from the cup forming a vacuum to draw the free piston using the reset piston to a ready to fire position; preventing travel of the free piston and pulling the reset piston from the cup thereby breaking the vacuum and accelerating the free piston to strike an anvil within an impact chamber to generate a sound pulse; transmitting the sound pulse through a fluid filled sound transmission chamber to an elastomeric bladder to propagate the pulse out and through the fluid filled bore hole and into the surrounding geological structures.

The method of generating a sound pulse within a bore hole may further comprise the steps of changing the viscosity and compressibility of fluid within the impact chamber to change the characteristics of the sound pulse. The method of generating a sound pulse within a bore hole may also further comprise the step of shaping a top surface of the anvil and the bottom surface of the free piston in reciprocal shapes to change the characteristics of the sound pulse. The method of generating a sound pulse within a bore hole may also further comprise the steps of shaping the top surface of the anvil to be a recessed cone and shaping the bottom surface of the free piston to be conical in shape to change the characteristics of the sound pulse. The method of generating a sound pulse within a bore hole may also further comprise the steps of transmitting a sound pulse wherein the free piston and anvil having flat surfaces; and collecting geological survey data; transmitting a sound pulse wherein the free piston having a conical shape and the anvil having a recess; collecting geological survey data; and combining the geological survey data acquired.

The method of generating a sound pulse within a bore hole may also further comprise the step of forming a dashpot in the anvil. The method of generating a sound pulse within a bore hole may also further comprise the step of enclosing the implosion chamber with an elastomeric bladder. The method of generating a sound pulse within a bore hole may also further comprise the step of enclosing the reservoir with an elastomeric bladder to form an expansion chamber. The method of generating a sound pulse within a bore hole may also further comprise the step forming the free piston with an annular rim.

These and other features, advantages and improvements according to this invention will be better understood by reference to the following detailed description and accompanying drawings. While references may be made to upper, lower, vertical and horizontal, these terms are used merely to describe the relationship of components and not to limit the operation of the present invention to any one orientation.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings in which:

FIG. 1A is a cross-sectional diagram of a first portion of a first embodiment of the impulse sound source of the present invention;

FIG. 1B is a continuation of the cross-sectional diagram of FIG. 1A as a second portion of a first embodiment of the impulse sound source of the present invention;

FIG. 2A is a cross-sectional diagram of a first portion of the first embodiment of the impulse sound source of the present invention;

FIG. 2B is a continuation of the cross-sectional diagram of FIG. 2A as a second portion of the first embodiment of the impulse sound source of the present invention;

FIG. 3 is a cross sectional diagram of cable termination of module A of the first embodiment of the impulse sound source of the present invention;

FIG. 4 is a cross sectional diagram of the expansion chamber of module B of the first embodiment of the impulse sound source of the present invention;

FIG. 5 is a cross sectional diagram of the electric motor of module C of the first embodiment of the impulse sound source of the present invention;

FIG. 6 is a cross sectional diagram of hydraulic fluid pump of module D of the first embodiment of the impulse sound source of the present invention;

FIG. 7A is a cross sectional diagram of the reset piston assembly and high pressure free piston chamber of module E of the first embodiment of the impulse sound source of the present invention in a ready to fire;

FIG. 7B is a cross sectional diagram of the reset piston assembly and free piston chamber of module E of the first embodiment of the impulse sound source of the present invention in a fired position;

FIG. 7C is a cross sectional diagram the reset piston assembly and free piston chamber of module E of the first embodiment of the impulse sound source of the present invention in an extension of the reset piston assembly to prepare the source for firing;

FIG. 7D is a top view cross section showing a first embodiment of the communication ports in the implosion chamber of module E in a first embodiment of the impulse sound source of the present invention;

FIG. 7E is a cross sectional diagram of a first embodiment of the latching seal flange of the reset piston assembly of module E of the first embodiment of the impulse sound source of the present invention;

FIG. 8 is a cross sectional diagram of the impact chamber of module F of the first embodiment of the impulse sound source of the present invention;

FIG. 9 is a cross sectional diagram is a further embodiment of the free piston and anvil of the impact chamber of module F of the first embodiment of the impulse sound source of the present invention;

FIG. 10A is a cross sectional diagram of the sound transmission chamber of module G of the first embodiment of the impulse sound source of the present invention; and

FIG. 10B is a top view cross section showing a first embodiment of communication ports in the sound transmission chamber of module G in a first embodiment of the impulse sound source of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The sleek design of the impulse sound source 1 provides for the insertion of the source into a bore hole for seismic analysis deep within the ground with an umbilical 2 extending to support and provide power and electronic control for the device. The impulse sound source 1 may be of any diameter and dimension suitable for the requirements of the geological survey with components of acceptable materials to withstand the high temperatures and pressures of a bore holes. In a first embodiment, the impulse sound source 1 is constructed with a series of modules as shown in FIGS. 1A and 1B with each of the modules A-G fixed end to end to one another along axis X using clamping rings and a series of bolt circles. Module A is the umbilical cable termination that as shown in FIGS. 2A and 2B has a housing 3 where the umbilical cable 2 aligns through the center of the housing and along axis X. The housing 3 may be of any shape, dimension or design with an upper termination head that is dependent on the size, design and construction of the umbilical cable 2. The umbilical cable 2 carries the weight of the source 1 as well as shields and surrounds the electric cables for power to the motor, and for electrical and/or optical cables for control and sensors as required within the source 1 such as sensors to determine the instant of firing, the pressure, the temperature and structural conditions within the source and within the bore hole.

As shown in FIG. 3, the connector 5 of module A provides a wire block 6 that distributes the electrical power, sensor and control cables throughout the source 1. Module A is attached to module B using a series of bolts 7 and a stainless steel clamping ring 4 positioned around the lower end of the cylindrical housing 3. Each of the upper and lower edges of the clamping ring 4 has a rim 8 extending completely around the ring 4 forming a channel 10 along a middle portion of the ring 4. The housing 3 and the rim 8 of the ring 4 may have a series of bolt holes 9 that are evenly spaced around the outer edge of the cylinder to accept the bolts 7 that secure the ring 4 to the housing 3. A groove 12 may be formed in the housing 3 to accept the rim 8 of the ring 4. The shoulder 14 forming the groove 12 may extend at a distance from axis X that is greater than a tubular center casing 15 that mates and aligns with the housing of module B. The tubular casing 15 formed on the base of the housing 3 is of a slightly smaller diameter than the diameter of the cylindrical housing 16 of module B. The housing 16 of module B, in this embodiment, is similarly formed with a shoulder 14 and groove 12 to provide for the lower rim 8 of the clamping ring 4 to lock around the shoulders 14 and secure the modules together. An index pin 18 may provide for the proper alignment and orientation of the modules with respect to one another. As described herein, heat resistant seal and bearing assemblies 20 made of viton or other plastic materials typically used in high pressure fluid applications are installed at the tubular casing 15 and at other connections in the housing and at each fluid path throughout the source to prevent leakage of hydraulic fluid and to properly secure and seal all high pressure connections.

Module B, as shown in FIG. 4, is an expansion chamber that is formed with a housing surrounded by an elastomeric bladder 21. The second half of the cable distribution connector 5 is a connector receptor 22 that is positioned at the top of the electric cable and fluid flow passage 24 that is formed through the center of the housing 16. The cable distribution connector 5 provides for the cable termination of module A to be disconnected from the rest of the impulse source for transportation of the source separate from the umbilical cable 2. The power cables 26 are properly shielded and extend down and through the fluid flow passage 24 to reach the motor cable connector 32 at the top of the motor 34 in module C. In a first embodiment, a combination time break pressure and temperature transducer 33 used to detect the firing of the source as well as monitor and transmit pressure and temperature is installed at the top of the fluid flow passage 24. Other sensors may be positioned throughout the source 1 to determine temperature and pressure as well as monitor and collect system operational parameters and other information. Module B also has openings 31 through the housing 16 to allow fluid communication from the flow passage 24 to the expansion chamber bladder 21. The flow passage 24 and expansion chamber 28 are filled with high temperature resistant hydraulic fluid to serve as a reservoir for the hydraulic pump 52 of module D of the source 1. The bladder 21 is secured to the housing 16 using band clamps 36 that surround the housing 16 and affix the bladder 21 at only the upper and lower portion of the housing 16 to allow for the middle of the bladder 21 to expand as pressure changes occur within the flow passage 24 and other modules of the source 1. A filler port 38 is provided to fill the flow passage 24. A vent 30 may be provided along the filler port passageway 29. A fluid passageway 40 is also provided at the base of module B to provide for communication of fluid between the flow passage 24 and the electric motor 34 of module C.

A housing 44, as shown in FIG. 5, surrounds the electrical motor 34 and an annular fluid flow compartment 42 is formed between the housing 44 and the module C outer housing 45. The compartment 42 is filled with the system hydraulic fluid from the upper passageway 40 from module B to help maintain the motor 34 at acceptable operational temperatures. The upper passageway 40 also provides for fluid to flow from the compartment 42 back through to the expansion chamber flow passage 24 of module B as the source is fired and pressures change within the source. As temperature and pressure increase or decrease within the source and fluid moves through the hydraulic system, the expansion bladder 21 expands or contracts to prevent damage to components within the source due to fluid fluctuations. At the base of the enclosure 44 a flow passage 47 connects the reservoir of Module B to the manifold block 54 of module D and a rubber or other durable shock absorbing material cushion mount 48 is placed to help isolate the motor 34 from accelerations caused by the motions of the free piston 43. The motor 34 is a reversible three phase or DC motor capable of high temperature operation. The motor housing 44 and other structural components of the source 1 may be of stainless steel or other comparable materials that are capable of sustaining the load and pressures of the firing of the source 1 and bore hole environment. At the base of the motor 34, the shaft 49 of the electric motor 34 extends along axis X into module D to operate the hydraulic fluid pump 52. The shaft 49 is aligned through the manifold block 54 and is affixed to the hydraulic pump 52 using a flexible coupling 56 as shown in FIG. 6.

The manifold block 54 is in the upper portion of module D and contains two check valves 58 and two pressure relief valves 60 for supplying the bi-directional hydraulic pump 52 with hydraulic fluid and for setting the maximum pressure at which the hydraulic system may operate. The manifold block 54 has fluid by-pass passages 62 that connect the pump 52 to the pressure relief valves 60 and bores 64 that communicate with fluid by-pass tubes 66 for delivering hydraulic fluid to the reset piston assembly chambers 63 and 65 of module E. The by-pass tubes 66 extend from an upper portion 67 of the housing 68 of module D to a lower portion 69 that forms a shoulder for the tubing connection. O-rings 61 are rabbited into recesses within the upper and lower housing 68 and 69 and each end of the by-pass tubes 66 are installed. This design feature provides easy access to the tubing 66 for repair. The upper surface 70 of the lower housing portion 69 forms a seat for bolts 7 to be inserted through bolt holes that are evenly spaced around the cylindrical housing for attachment of module D to module E.

As the motor shaft 49 rotates in one direction, fluid is delivered to one by-pass passage 62 and one by-pass tube 66 and fluid is returned through the other by-pass tube 66 and by-pass passage 62 thereby simultaneously filling one and evacuating the other of the reset piston chambers 63 and 65 to extend or retract the reset piston assembly of module E. The check valves 58 direct fluid flow based on the rotational direction of the motor 34. The relief valves 60 provide for the release of fluid back to the reservoir of module B to prevent over pressuring the system as the reset piston assembly reaches a full point of extension and bottoms out in the receiving cup 130 of the free piston 110 or full retraction at an upper most point with the motor continuing to run in one direction until a peak in amperage triggers a relay switch (not shown) to change the direction of flow.

As shown in FIG. 6, the rod 72 of the reset piston assembly extends into a cavity 74 formed by the housing 68 of module D. In order to slide smoothly a bearing and seal assembly is installed within bulkhead 75. The bearing and seal assembly includes a seal 71 a bearing 73 and a backup ring 78 positioned to protect the seal 71 from extrusion. To secure the bearing and seal assembly in place a retainer ring 82 is installed between a preformed edge 77 at the base of the housing 68 and a ledge formed at the upper surface 79 of the upper housing 80 of module E. The seal 71 prevents fluid leakage from chamber 63 into cavity 74 as chamber 63 is pressurized.

The reset piston 84 separates chambers 63 and 65 and is positioned along the piston rod 72 using a cylindrical sheath 83 and cap nut 85 that is tightened to hold the reset piston 84 in place along the rod 72. The sheath 83 is set at a thickness t that when combined with the upper rod diameter d is equal to the lower rod diameter D below the piston 84 in order to maintain an equal volume in the actuation chamber 63 and retraction chamber 65 above and below the piston 84. Hydraulic fluid from the hydraulic pump 52 is fed to and returned from the actuation chamber 63 through actuation feed bore 87. Hydraulic fluid is fed to and returned from the retraction chamber 65 through feed bore 89. A seal gland and ring bearing assembly 86 is affixed to the outer diameter of the reset piston 84 to seal and further assist in the reduction of friction as shown in FIG. 7A. The housing 80 of module E encloses the reset piston actuation chamber 63 and retraction chamber 65 with bulkhead 76 forming the base of the retraction chamber 65. The housing 80 is enclosed by an elastomeric bladder 102 forming the high pressure fluid implosion chamber 100 for the free piston 110. The free piston 110 may be hollow to reduce the weight of the free piston 110 and the overall weight of the source 1.

The bladder 102 is affixed to the housing at each end of the module using band clamps 36. The chamber 100 is sealed using a seal gland and ring bearing assembly 94 at bulkhead 76 that provides for reduced friction allowing the piston rod 72 to move smoothly between the reset piston chamber and implosion chamber. For the communication of fluid to and from the actuation and retraction feed lines 87 and 89 bores may be drilled through the housing and resealed with a brazed plug 96. A fluid fill plug 98 that is for example 90 degrees away from the actuation and retraction feed lines 87 and 89 is provided to fill the implosion chamber 100 with hydraulic fluid.

The housing 80 of the implosion chamber 100 may be tapered at either end to provide support structures for the attachment of bolts 7 to connect module D at the upper support structure 104 and to connect module F at the lower support structure 106 along the axis X. A seal gland ring bearing assembly 112 is installed at the lower support structure 106 to seal the implosion chambers and reduce friction to allow the free piston 110 to move smoothly within the impact chamber 120 of module F. The module F housing 118 surrounds the free piston 110 to form the impact chamber 120. Additional seals 20 are installed between the support bulkhead 118 and lower structural support 106 of housing 80 to prevent leakage. A fluid fill plug 128 as shown extends from the impact chamber perpendicularly to axis X and through the support bulkhead 118 to fill the impact chamber 120 to an appropriate fluid level denoted as fin FIG. 7A.

As shown in FIG. 7A, the piston rod 72 extends out and through the actuation and retraction chambers 63 and 65 and the chamber bulkhead 76. Attached to the end of the reset piston rod 72 is the reset piston latching seal assembly 123 that using a vacuum seal retains and draws the free piston 110 to a ready to fire position at an uppermost point within the implosion chamber 100. At the highest retraction point of the reset piston 84, the upper circular surface 151 of the receiving cup 130 strikes a shoulder 152 of the housing 80 that pulls the latching seal 146 out of the cup 130 breaking the vacuum seal and providing for high pressure fluid to flow past the latching seal 146 to rapidly accelerate the free piston through the chamber 100 to contact the anvil 160 within the impact chamber 120 transmitting the sound pulse as shown in FIG. 7B. A cross-sectional top view of the housing 80 showing the central portion of the implosion chamber 100 and the ports 90 that provide communication between the chamber 100 and the elastomeric bladder 102 is shown in FIG. 7C.

The source 1 is prepared for firing by filling the actuation reset piston chamber 63 with pumped pressurized hydraulic fluid to force the reset piston 84 and the latching seal assembly 123 from the upper retraction position after firing down and into the receiver cup 130 of the free piston 110 at the base of the implosion chamber 100, as shown in FIG. 7D. The latching seal assembly 123 plugs into the receiver cup 130 formed in the upper portion at the top of the free piston 110, and is retained within the receiver cup 130 due to the evacuation of fluid that is trapped within the space between the bottom cylindrical surface 145 of the reset piston flange 138 that includes the reset piston latching seal assembly 123 and the upper cylindrical surface 148 of the cup 130. The fluid within this space is purged out through a passageway 132 forcing check valve 134 to open and release the evacuated fluid into the implosion chamber 100 through the check valve outlet 135. The evacuated space forms a vacuum to effectively lock the latching seal assembly flange 138 and free piston 110 together. Hydraulic fluid is then simultaneously removed from the actuation chamber 63 and fed to the retraction chamber 65 to draw the free piston 110 up to an uppermost retraction point in the implosion chamber 100.

The latching seal assembly 123, as shown in FIG. 7E, has a high pressure latching seal ring 146 that surrounds the flange 138. The flange 138 has a diameter with a very close tolerance to and only slightly smaller than the diameter of the receiving cup 130 with the latching seal ring 146 seated within a groove formed around the outer diameter of the flange 138 and extending out beyond the edge 142 of the outer diameter of the flange 138. In a first embodiment, the latching seal 146 is retained within this groove in the flange a hooked sealing surface 141 and using a seal retainer ring 143 with flat head screws 144 that may be inserted through the base 145 of the flange 138 and be countersunk to maintain a smooth surface of the base 145 to mate with the smooth surface 148 of the receiving cup 130. Alternatively, the retaining ring 143 and screws 144 may be inserted through the upper surface 147 of the flange 138 to retain the latching seal 146. The retainer ring 143 may have a similar hooked surface 139 to retain the seal 146. Check valve 134 is mounted within the center and flush to the base 145 of the flange 138 by inserting a spanner wrench in slots 133 on either side of a central fluid passageway 132. The outlet port 135 of the check valve 134 communicates with the implosion chamber 100 and provides for fluid in the space between the base 145 of the reset piston assembly flange 138 and the inner cylindrical surface 148 of the receiving cup 130 to be evacuated through the passageway 132 and open check valve 134 to create the vacuum seal that retains and draws the free piston 110 into the ready to fire position. A pressure relief outlet 92 may be formed through the reset piston assembly housing 80.

As an example, if all or nearly all of the fluid has been purged out of the space between the bottom surface 145 of the piston flange 138 and the inner surface 148 of the free piston cup 130 through the check valve 134 and given that the sealing diameter at the inside diameter ID of the receiving cup 130 of the free piston 110 is 8.9 cm (3.5 inches) and the diameter of the portion of the reset piston assembly flange 138 within the receiving cup 130 is 7.6 cm (3.0 inches), the difference in effective cross sectional area at the annular rim 149 of the receiving cup 130 is 6.5 cm² (2.56 square inches). Therefore, if the fluid pressure within the implosion chamber 100 is 20.6 MPa (3000 psi) then as the reset piston assembly flange 138 moves upward compressing the fluid within the implosion chamber 100, the 6.5 cm² (2.56 square inch) difference in area produces a clamping force approaching 34.2 kN (7680 pounds of force) between the flat surfaces. This clamping force provides for the reset piston assembly to draw the free piston 100 to the full retraction point of the reset piston assembly. At the top of the retraction stroke of the reset piston 84, the upper edge 151 of the receiving cup 130 of the free piston 110 is stopped against the bottom side of a shoulder 152 formed in the implosion chamber housing 80 and the latching seal assembly flange 138 begins to pull out of the receiving cup 130. The expanded diameter of the latching seal 146 is pulled past a radius 154 formed in the vertical wall of the cup 130 releasing the vacuum and allowing fluid within the chamber 100 to flow past the latching seal 146 and fill the evacuated space between the upper and lower surfaces 145 and 148 accelerating the free piston 110 rapidly towards the impact chamber 120.

The impact chamber 120, as shown in FIG. 8, is partially filled with fluid to cushion the impact between the metal impact surface 162 of the free piston 110 and the anvil face 164. The compressibility and viscosity of the fluid within the impact chamber 120 and the shape of the impact surface 162 and anvil face 164 all contribute to the quality and characteristics of the sound produced by the impulse source 1. Upon impact, the anvil piston 160 within the cylindrical support bulkhead 118 of module F and partially into an upper portion 172 of the sound transmission chamber 170 of module G. The support bulkhead 118 includes two bolting flanges 124 and 125 that extend laterally to provide bolt holes that are evenly spaced around the circular upper flange 124 attaching module E to module F and the circular lower flange 125 attaching module F to module G.

A dashpot nose 166 is formed at the cylindrical base 168 of the anvil piston 160. The cushion profile of the dashpot 166 is formed to act as a damper to absorb the remaining energy of the anvil 160 as it stops moving at the bottom of its impulse stroke. A seal and bearing assembly 178 is installed on the anvil piston 160 to reduce friction and a ring seal 179 is installed on the bulkhead 118 to prevent fluid flow between the impact chamber 120 and sound transmission chamber 170.

After firing, the impact chamber fluid is forced through a channel 180 formed through the anvil piston 160 and into a by-pass passageway 181 and into the space 182 within the impact chamber 120 created by the movement of the anvil piston 160 of module F. In drawing the free piston 110 up to the reset position for firing, fluid is drawn from the space 182 and up through the channel creating a vacuum and drawing the lower anvil piston 160 up and into the impact position for firing. The source 1 may be of any acceptable shape and dimension to accommodate the shape and dimensions of the bore hole being surveyed. As shown in FIG. 9, the free piston 110 may be shaped as a conical point 163 and the anvil may have a cylindrical opening 177 that would cause the frequency content to change as the conical point 163 enters the opening 177 producing a longer pulse with lower frequency content in the sound pulse. The free piston 110 and anvil may be formed in various shapes to produce a range of amplitudes and frequencies.

A fill valve 184 and passage 186 is provided for module G to fill and adjust the fluid within the sound transmission chamber 170. A bladder 188 is affixed to the upper portion and lower portion of the sound transmission housing 176 as shown in FIG. 10A using band clamps 36. Any number of ports 190 to transfer fluid from the sound transmission chamber 170 to the bladder 188 may be formed within the sound transmission chamber housing 176 with the number and dimensions dependent on the requirements of the geological survey. As noted, because of the modularity of the source 1, module G may be replaced with a sound transmission chamber having more or less than the four ports shown from the top view of the sound transmission chamber in FIG. 10B. A time break transducer or other sensors 33 may be installed in the sound transmission chamber 170 to detect the firing of the source or pressures and temperatures within the source 1. In a first embodiment, the end 194 of module G may be conically in shape to prevent the source from being held or damaged on ledges within the bore hole as the source is inserted and hung from the umbilical cable 2.

In operation, the source 1 in its ready to fire position is shown in FIG. 7A, in its fired position is shown in FIG. 7B and in its reset position is shown in FIG. 7D being picked up by the reset piston latching seal assembly 123. As the latching seal assembly flange 138 plugs into the receiving cup 130 at the top of the free piston 110, the latching seal 146 seals and slides within the bore of the cup 130. Fluid within the cup 130 escapes out through the check valve 134 forming a partial vacuum with the clamping force of the high pressure fluid within the implosion chamber 100 holding the reset piston latching seal assembly 123 and the interior surface 148 of the cup portion 130 together to draw the free piston 110 to the retraction point where the upper edge 151 of the free piston 110 is stopped against the shoulder 152 formed within the reset piston assembly housing 80. The latching seal assembly flange 138 is partially pulled from the cup 130, fluid enters past the radius 154 formed in the outer edge of the cup 130 and past the latching seal 146 to fill the evacuated space between the flat surfaces 145 and 148 of the latching seal assembly flange 138 and the free piston 110 releasing the vacuum and accelerating the free piston 110 down to impact upon the sound transmitting anvil piston 160 sending a sound pulse into chamber 170, through ports 190 to the bladder 188 and out through the ambient wall of fluid within the bore hole and into the surrounding geological structures.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 

What is claimed is:
 1. An impulse sound source, comprising: an umbilical cable extending through a cylindrical housing; a hydraulic fluid reservoir formed within the housing and supplying an hydraulic pump; an electric motor powered from the umbilical cable and controlling the hydraulic pump; a hydraulic cylinder controlled by the hydraulic pump; a reset piston movable within a fluid filled piston chamber using the hydraulic cylinder, the reset piston having a flange movable within an implosion chamber; a free piston having an annular rim and cup within the implosion chamber; an anvil within an impact chamber adjacent the implosion chamber; an elastomeric bladder enclosing a fluid filled sound transmission chamber adjacent the impact chamber; and wherein the free piston is accelerated by hydrostatic pressure within the implosion chamber to strike the anvil and transmit a sound pulse through the sound transmission chamber and the elastomeric bladder.
 2. The impulse sound source of claim 1 further comprising a latching seal assembly surrounding the reset piston flange, the flange having an inlet passage and check valve to evacuate fluid from the free piston cup and thereby latch the reset piston and free piston to draw the free piston to a ready to fire position.
 3. The impulse sound source of claim 2 wherein the difference in cross-sectional area of the reset piston flange and free piston annular rim provides the clamping force for the reset piston to latch to the free piston.
 4. The impulse sound source of claim 3 wherein the sound source is repeatably fired by having the reset piston retract to an uppermost position causing the electric motor to rotate in a first direction to control the delivery of hydraulic fluid from the hydraulic pump to a first chamber and return hydraulic fluid to the reservoir from a second chamber and move the reset piston to the free piston; and wherein the reset piston and free piston latch triggering the electric motor to reverse direction and the delivery of hydraulic fluid from the hydraulic pump is to the second chamber and return of hydraulic fluid to the reservoir is from the first chamber to move the reset piston and free piston to the uppermost position where the free piston is fired and the electric motor is triggered to rotate in the first direction.
 5. The impulse sound source of claim 4 wherein the impact chamber is partially filled with fluid and changing the viscosity and compressibility of the fluid within the impact chamber changes the characteristics of the sound pulse.
 6. The impulse sound source of claim 5 wherein the shape of a bottom surface of the free piston and the shape of the top surface of the anvil changes the characteristics of the sound pulse.
 7. The impulse sound source of claim 6 wherein the top surface of the anvil is recessed in shape and the shape of the free piston is conical.
 8. The impulse sound source of claim 1 wherein the anvil further comprising a dashpot.
 9. The impulse sound source of claim 1 wherein the implosion chamber further comprising an elastomeric bladder to conform to fluid movements within the impulse sound source.
 10. The impulse sound source of claim 1 wherein the reservoir further comprising an elastomeric bladder to conform to fluid movements within the impulse sound source.
 11. The impulse sound source of claim 1 wherein the components are arranged in the order of an umbilical termination module on the top, an expansion chamber module beneath, next an electric motor housing module beneath, next a hydraulic pump module beneath, next an hydraulic cylinder module beneath, next a free piston implosion module beneath, next an impact chamber module beneath, and next a sound transmitting module beneath.
 12. The impulse sound source of claim 1 further comprising a manifold block adjacent to the hydraulic pump.
 13. The impulse sound source of claim 12 wherein the manifold block houses two pressure relief valves and two check valves.
 14. The impulse sound source of claim 1 wherein the reset piston is directly attached to a hydraulic piston rod on the opposite side of a hydraulic cylinder bulkhead
 15. The impulse sound source of claim 1 wherein the sound transmitting anvil has fluid flow passages for fluid volume control.
 16. A method of generating a sound pulse within a bore hole, comprising the steps of: extending an umbilical cable to support a cylindrical housing of a sound source; storing hydraulic fluid in a reservoir within the housing; supplying a hydraulic pump from the reservoir; controlling the hydraulic pump using an electric motor powered from the umbilical cable; filling a hydraulic cylinder using the hydraulic pump; moving a reset piston within a fluid filled implosion chamber using the hydraulic cylinder; seating the reset piston within a cup formed in the upper portion of a free piston; evacuating fluid from the cup forming a vacuum to draw the free piston using the reset piston to a ready to fire position; preventing travel of the free piston and pulling the reset piston from the cup thereby breaking the vacuum and accelerating the free piston to strike an anvil within an impact chamber to generate a sound pulse; transmitting the sound pulse through a fluid filled sound transmission chamber to an elastomeric bladder to propagate the pulse out and through the fluid filled bore hole and into the surrounding geological structures.
 17. The method of generating a sound pulse within a bore hole of claim 16 further comprising the steps of changing the viscosity and compressibility of fluid within the impact chamber to change the characteristics of the sound pulse.
 18. The method of generating a sound pulse within a bore hole of claim 16 further comprising the step of shaping a top surface of the anvil and the bottom surface of the free piston in reciprocal shapes to change the characteristics of the sound pulse.
 19. The method of generating a sound pulse within a bore hole of claim 16 further comprising the steps of shaping the top surface of the anvil to be a recessed cone and shaping the bottom surface of the free piston to be conical in shape to change the characteristics of the sound pulse.
 20. The method of generating a sound pulse within a bore hole of claim 16 further comprising the steps of transmitting a sound pulse wherein the free piston and anvil having flat surfaces; and collecting geological survey data.
 21. The method of generating a sound pulse within a bore hole of claim 20 further comprising the steps of transmitting a sound pulse wherein the free piston having a conical shape and the anvil having a recess; collecting geological survey data; and combining the geological survey data of claim 20 with the acquired geological survey data.
 22. The method of generating a sound pulse within a bore hole of claim 16 further comprising the step of forming a dashpot in the anvil.
 23. The method of generating a sound pulse within a bore hole of claim 16 further comprising the step of enclosing the implosion chamber with an elastomeric bladder.
 24. The method of generating a sound pulse within a bore hole of claim 16 further comprising the step of enclosing the reservoir with an elastomeric bladder to form an expansion chamber.
 25. The method of generating a sound pulse within a bore hole of claim 16 further comprising the step forming the free piston with an annular rim. 